This invention relates to a unijunction transistor (UJT). More specifically, it relates to a replacement circuit for a UJT.
A UJT is a three-terminal semiconductor device having electrical characteristics and, therefore, functional applications which are very different from those of conventional two-junction transistors. The features of the UJT most useful to circuit designers are a negative-resistance characteristic over a region of operation, a stable firing voltage, a low firing current, and a high pulse-current capability. Resulting from these characteristics, the UJT finds applications in oscillators, timing circuits, voltage sensing circuits, SCR firing circuits and bistable circuits.
In the semiconductor industry, the demand for UJTs has fallen dramatically as a result of the availability of newer components, for example, the 555 timer. In response, the manufacturers of these devices have either discontinued their products or, in making their products, switched from handmade fabrication techniques to more effective semiconductor fabrication techniques, such as diffusion methods.
As a result, a recently fabricated UJT does not always meet its original performance specifications. Specifically, currently available UJTs exhibit wide variations in their peak-point, leakage current and maximum oscillation frequency characteristics.
This presents a problem in the use of a UJT in an electronic circuit design which relies on the originally specified performance of the UJT. To obtain an operational UJT that will support such circuits, engineers have had to resort to performing special device screening tests on every UJT received, wherein each UJT is tested to ensure compliance with performance specifications. A typical yield from the screenings has been 10 percent, a very low yield. The engineering and manufacturing costs associated with the further use of these components in accordance with their original specifications are, therefore, increasing.
A replacement circuit having the original performance characteristics of a UJT, therefore, is needed.